Ubuntu 16.04 and Eclipse Mars 2 , virtual webdav mounting problem

I built the cryptomator with eclipse Mars 2 in Ubuntu 16.04,
I create a vault, after that I try to open the created vault, but mounting encountered to problem, and no virtual vault is appear for me!!
The logs appear in eclipse console are as follow:

[JavaFX Application Thread] ERROR org.cryptomator.ui.util.AsyncTaskService - Uncaught exception java.lang.NullPointerException: null at org.cryptomator.frontend.webdav.mount.MountParams$MountParamsBuilder.withWindowsDriveLetter(MountParams.java:28) at org.cryptomator.ui.model.Vault.mount(Vault.java:141) at org.cryptomator.ui.controllers.UnlockedController.lambda$1(UnlockedController.java:164) at org.cryptomator.ui.util.AsyncTaskService.lambda$0(AsyncTaskService.java:43) at org.cryptomator.ui.util.AsyncTaskService$AsyncTaskImpl.lambda$6(AsyncTaskService.java:106) at org.cryptomator.ui.util.AsyncTaskService.logExceptions(AsyncTaskService.java:135) at org.cryptomator.ui.util.AsyncTaskService.access$3(AsyncTaskService.java:133) at org.cryptomator.ui.util.AsyncTaskService$AsyncTaskImpl.lambda$4(AsyncTaskService.java:104) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:748)

how can I fix it?

Answered in https://github.com/cryptomator/cryptomator/issues/583#issuecomment-330495721